Field of the Invention
The present invention relates to a door operator system and particularly, to a door operator system capable of detecting a current-time position of a movable barrier.
Description of the Related Art
Generally, a conventional door operator is capable of completely opening a door or completely shutting the door by determining whether an upper stop point or a lower stop point of a movable barrier is reached or not. That is to say, the movable barrier can be stopped or held only at the upper stop point or the lower stop point. However, for some special purposes, the movable barrier is required to be stopped or held at a midway position between the upper stop point and the lower stop point.
U.S. Pat. No. 7,161,100 proposes a limit switch mechanism having a screw rod coupled to a winding shaft, wherein the screw rod is provided with two switch actuators thereon. The switch actuators are moved along the screw rod while the screw rod is rotated along with the winding shaft. If one of the switch actuators triggers a corresponding limit switch at the end of the screw rod, the triggered limit switch signals to the door operator that the upper stop point or the lower stop point is reached, thereby disabling the door operator.
However, as stated above, due to the intrinsic structure of this kind of prior art door operation, the conventional door operator is capable of determining whether the upper stop point or the lower stop point of the movable barrier is reached or not but incapable of detecting a current-time position of the movable barrier at any time. As such, the conventional door operator is incapable of stopping or holding the movable barrier at a midway position. In the case that at least one limit switch is in failure, the electric motor of the door operator may be still electrically energized even if the upper stop point or the lower stop point has been reached so that the components of the door operator may be damaged.
A variable frequency motor is a motor capable of operating at a variable speed, for example a descending speed or an ascending speed. Use of the variable frequency motor in the door operator is desired, but the absence of capability of detecting a current-time position of a movable barrier makes the use of the variable frequency motor in the door operator difficult.